It is widely known to drive spring loaded poppet valves of combustion engines, hereinafter named engine valves, by means of a hydraulic pressure pulse generator. For example, U.S. Pat. No. 6,067,946 discloses the opening of an engine valve by an application of a hydraulic pressure onto a piston that is connected to the valve. The hydraulic pressure either comes from a high pressure source or a low pressure source. The application of the hydraulic pressure is performed by means of a pressure control device based upon signals that are received from an electronic control member. The hydraulic pressure is applied in such a way as to minimize the energy that is required for the activation of the valve while, at the same time, the inertia of the valve is taken ad vantage of. The described system comprises means for opening/interrupting the communication between the high pressure source and the chamber in which the piston is arranged, and means for opening/interrupting the communication between the low pressure source and said chamber.
The method disclosed in U.S. Pat. No. 6,067,946 includes that the high pressure source is brought in the communication with the chamber while the valve is displaced in a direction out of the chamber, i.e. to the opening position of the valve. When the valve gets close to a maximally open position, the communication between the chamber and the high pressure source is interrupted and, instead, a communication between the chamber and the low pressure source is opened. In that way, a braking of the valve is accomplished before it reaches its end position. When the valve has reached this position, it can be locked in that position by interrupting both of said communications. When the valve is to return to its closed position, the communication between the low pressure source and the chamber is re-opened, whereby the pre-loaded spring force displaces the piston into the chamber. When the valve is close to its closed position, the home position, the communication between the high pressure source and the chamber is opened and the communication between the low pressure source and the chamber is interrupted. In that way, a braking of the movement in this direction is achieved. When the valve has reached its home position both communications may be interrupted to keep the valve in this position. In this way, the time during which the valve is open is controlled.
The drawback of this prior art is that the hydraulic liquid which comes from the high pressure source and is used for the projection of the valve to the open position thereof is almost completely further conducted to the low pressure source, whereby there is a significant loss of energy.